1. Field of the Invention
The present invention relates to a composition comprising aromatic carboxylic acid compounds that is capable of effectively serving as a color developer, and a thermosensitive recording material comprising the above-mentioned composition.
2. Discussion of Background
Generally, a thermosensitive recording material comprises a support and a thermosensitive coloring layer formed thereon, which comprises as the main components a colorless or light colored electron-donating dye precursor, and an electron-accepting color developer. These dye precursor and color developer are caused to react instantaneously upon the application of heat thereto to produce recorded images, for instance, using a thermal head, heat pen or laser beam, as disclosed in Japanese Patent Publications 43-4160 and 45-14039.
A thermosensitive recording material is used in a wide variety of fields, for example, as the recording material for an electronic computer, facsimile machine, ticket vending machine, label printer, and recorder because it has the advantages that recording can be achieved using a relatively simple apparatus, maintenance is simple, and there is no noise development.
The above-mentioned thermosensitive recording material employing such an electron-donating dye precursor and an electron-accepting color developer has excellent characteristics such as good appearance and nice touch and is capable of producing images with high coloring density. On the other hand, such a recording material has the disadvantage that the preservation stability of the recorded images is poor. To be more specific, when image areas formed in the thermosensitive recording material come in contact with plastics such as polyvinyl chloride, the image areas are decolorized by the influence of a plasticizer and other additives contained in the plastics. When the colored image areas come in contact with chemicals contained in foods or cosmetics, such image areas are also easily decolorized or the background area easily causes color development.
To improve the preservation stability of the image recorded in the thermosensitive recording material, various color developers with high reliability are conventionally proposed. For instance, the use of a phenolsulfone compound as the color developer is disclosed in Japanese Laid-Open Patent Applications 58-82788 and 60-13852; and the use of a substituted salicylic acid compound, disclosed in Japanese Laid-Open Patent Application 62-169681. However, even though the aforementioned compounds are used as the color developers, the image area formed in the thermosensitive recording material shows still insufficient fastness to plasticizers.
It is therefore a first object of the present invention to provide a color developer capable of producing colored image areas with improved preservation stability, particularly, in terms of the plasticizer resistance and the oil resistance of the produced image.
A second object of the present invention is to provide a thermosensitive recording material comprising the above-mentioned color developer.
The first object of the present invention can be achieved by a composition comprising at least two aromatic carboxylic acid compounds selected from the group consisting of aromatic carboxylic acid compounds of formulas (I), (II) and (III): 
wherein X represents carbonyl group; sulfonyl group; a bivalent group derived from an aliphatic hydrocarbon; a bivalent group derived from an aliphatic hydrocarbon comprising in the main chain thereof at least one hetero atom, carbonyl group, sulfonyl group, an ester linkage, or an aromatic ring; or a bivalent group derived from an aromatic hydrocarbons compound prepared by connecting two aromatic hydrocarbons via at least one hetero atom, carbonyl group, sulfonyl group, an ester linkage, an alkylene, or an aliphatic hydrocarbon comprising a hetero atom in the main chain thereof.
In the formulas (I) to (III), it is preferable that the bivalent functional group represented by X have the following formula (IV): 
wherein R and Rxe2x80x2 which may be the same or different are each a hydrogen atom, a halogen atom, an alkyl group having 1 to 8 carbon atoms, an aralkyl group having 1 to 8 carbon atoms, or an aryl group having 1 to 8 carbon atoms; n is an integer of 1 to 4; m is an integer of 0 or 1; and A and B are each carbonyl group, sulfonyl group, a bivalent group derived from an aliphatic hydrocarbon, a bivalent group derived from an aliphatic hydrocarbon comprising in the main chain thereof at least one hetero atom, carbonyl group, sulfonyl group, an ester linkage, or an aromatic ring, or a bivalent group derived from an aromatic hydrocarbon compound prepared by connecting two aromatic hydrocarbons via at least one hetero atom, carbonyl group, sulfonyl group, an ester linkage, an alkylene, or an aliphatic hydrocarbon comprising a hetero atom in the main chain thereof.
Furthermore, it is preferable that the bivalent functional group represented by B in formula (IV) be sulfonyl group.
In addition, it is preferable that the bivalent functional group represented by X in formulas (I) to (III) be derived from a bivalent group selected from the group consisting of an alkylene, oxyalkylene, thioalkylene, sulfinylalkylene, and sulfonylalkylene, each having 1 to 16 carbon atoms.
The above-mentioned second object of the present invention can be achieved by a thermosensitive recording material comprising a support and a thermosensitive coloring layer formed thereon comprising a leuco dye and a color developer capable of inducing color formation in the leuco dye upon application of heat thereto, with the color developer comprising a composition comprising at least two aromatic carboxylic acid compounds selected from the group consisting of aromatic carboxylic acid compounds of the previously mentioned formulas (I), (II) and (III).
The composition according to the present invention comprises at least two aromatic carboxylic acid compounds selected from the group consisting of aromatic carboxylic acid compounds represented by the aforementioned formulas (I), (II) and (III).
The reasons why the above-mentioned composition of the aromatic carboxylic acid compounds can impart high plasticizer resistance and oil resistance to the colored images formed in the thermosensitive recording material have not yet been clarified, but are considered to be as follows:
(1) The composition of the present invention is provided with excellent color developing capability because the aromatic carboxylic acid compound of formula (I), (II) or (III) contained in the composition is a strong acid having an electron attractive group as the substituent.
(2) The solubility of the aforementioned composition in nonvolatile solvents such as oils and plasticizers can be lowered. This is because the molecular weight of each aromatic carboxylic acid compound is increased by including two or more aromatic carboxylic acids in the molecule thereof.
The composition comprising at least two aromatic carboxylic acid compounds according to the present invention is novel. This composition can be obtained by esterification reaction between a trimellitic acid anhydride and an alcohol compound, for example, in accordance with the following reaction scheme: 
More specifically, the composition of the present invention is obtained in the form of a mixture of at least two aromatic carboxylic acid compounds with carboxyl groups being substituted at different positions, that is, isomers, through the above-mentioned reaction. Namely, there can be obtained a composition comprising the aromatic carboxylic acid compounds of formulas (I) and (II); a composition comprising the aromatic carboxylic acid compounds of formulas (II) and (III); a composition comprising the aromatic carboxylic acid compounds of formulas (I) and (III); and a composition comprising the aromatic carboxylic acid compounds of formulas (I), (II) and (III). Any of the above-mentioned compositions can be used as the color developer for use in the thermosensitive recording material. When necessary, the composition may be separated into the above-mentioned isomers, for example, by recrystallization or chromatography.
Specific examples of the bivalent functional group represented by X in the formulas (I), (II) and (III) include an alkylene, oxyalkylene, bisoxyalkylene, trisoxyalkylene, oxoalkylene, bisoxoalkylene, trisoxoalkylene, thioalkylene, bisthioalkylene, tristhioalkylene, sulfinylalkylene, bissulfinylalkylene, trissulfinylalkylene, sulfonylalkylene, bissulfonylalkylene, trissulfonylalkylene, hydroxyalkylene, bishydroxyalkylene, trishydroxyalkylene, sulfonyldioxyalkylene, bissulfonyldioxyalkylene, trissulfonyldioxyalkylene, carbonyldioxyalkylene, biscarbonyldioxyalkylene, triscarbonyldioxyalkylene, carbamoylalkylene, biscarbamoylalkylene, and triscarbamoylalkylene, each having 1 to 16 carbon atoms.
Further, examples of the bivalent functional group represented by X in the formulas (I), (II) and (III) are as follows: 
In the formulas (IV) to (VII), R and Rxe2x80x2 which may be the same or different are each a hydrogen atom, a halogen atom, an alkyl group having 1 to 8 carbon atoms, an aralkyl group having 1 to 8 carbon atoms, or an aryl group having 1 to 8 carbon atoms; and n is an integer of 1 to 4.
Specific examples of the bivalent group represented by A in the above-mentioned formulas (IV) and (VI) include an alkylene, oxyalkylene, bisoxyalkylene, trisoxyalkylene, oxoalkylene, bisoxoalkylene, trisoxoalkylene, thioalkylene, bisthioalkylene, tristhioalkylene, sulfinylalkylene, bissulfinylalkylene, trissulfinylalkylene, sulfonylalkylene, bissulfonylalkylene, trissulfonylalkylene, hydroxyalkylene, bishydroxyalkylene, trishydroxyalkylene, sulfonyldioxyalkylene, bissulfonyldioxyalkylene, trissulfonyldioxyalkylene, carbonyldioxyalkylene, biscarbonyldioxyalkylene, triscarbonyldioxyalkylene, carbamoylalkylene, biscarbamoylalkylene, and triscarbamoylalkylene, each having 1 to 16 carbon atoms.
With respect to B in the aforementioned formulas (IV) and (V), m is an integer of 0 or 1. When m is an integer of 1, specific examples of the group represented by B in the aforementioned formulas (IV) and (V) are oxygen atom, carbonyl group, sulfur atom, sulfinyl group, sulfonyl group, sulfonyloxy group, carbonyloxy group, carbonylamino group, urea group, hydrazinocarbonyl group, hydrazinosulfonyl group, phenylene, biphenylene, xylylene, 
Furthermore, there can be employed as the bivalent group represented by B in the formulas (IV) and (V) an alkylene, oxyalkylene, bisoxyalkylene, trisoxyalkylene, oxoalkylene, bisoxoalkylene, trisoxoalkylene, thioalkylene, bisthioalkylene, tristhioalkylene, sulfinylalkylene, bissulfinylalkylene, trissulfinylalkylene, sulfonylalkylene, bissulfonylalkylene, trissulfonylalkylene, hydroxyalkylene, bishydroxyalkylene, trishydroxyalkylene, sulfonyldioxyalkylene, bissulfonyldioxyalkylene, trissulfonyldioxyalkylene, carbonyldioxyalkylene, biscarbonyldioxyalkylene, triscarbonyldioxyalkylene, carbamoylalkylene, biscarbamoylalkylene, and triscarbamoylalkylene, each having 1 to 16 carbon atoms.
For instance, when the bivalent group X in the formulas (I), (II) and (III) is xe2x80x94C2H4xe2x80x94, that is represented by the example No. (1) for convenience, there can be obtained a composition comprising at least two aromatic carboxylic acid compounds selected from the group consisting of the following three isomers of formulas (1-I), (1-II), and (1-III): 
Other examples of the bivalent group X are shown in TABLE 1, and in each case, there can be similarly obtained a composition comprising at least two aromatic carboxylic acid compounds selected from the group consisting of the three isomers as represented by the formulas (1-I) to (1-III).
When the above-mentioned composition of aromatic carboxylic acid compounds represented by formulas (I) to (III) is contained in the thermosensitive coloring layer, it is preferable that the amount of the composition be in the range of 1 to 10 g/m2, more preferably in the range of 1 to 5 g/m2 on a dry basis.
The above-mentioned basic dye precursors such as leuco dyes can be used alone or in combination together with the color developer in the thermosensitive coloring layer. Any leuco dyes that are conventionally employed in the thermosensitive recording material are usable in the present invention.
Specific examples of the leuco dyes are as follows:
3,3-bis(p-dimethylaminophenyl)phthalide,
3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide,
3-diethylamino-6-methyl-7-anilinofluoran,
3-dibutylamino-6-methyl-7-anilinofluoran,
3-N-methyl-N-butylamino-6-methyl-7-anilinofluoran,
3-N-methyl-N-propylamino-6-methyl-7-anilinofluoran,
3-N-ethyl-N-propylamino-6-methyl-7-anilinofluoran,
3-N-methyl-N-amylamino-6-methyl-7-anilinofluoran,
3-N-ethyl-N-amylamino-6-methyl-7-anilinofluoran,
3-N-ethyl-N-isoamylamino-6-methyl-7-anilinofluoran,
3-N-hexyl-N-isoamylamino-6-methyl-7-anilinofluoran,
3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluoran,
3-N-ethyl-N-furanylmethylamino-6-methyl-7-anilinofluoran,
3-diethyl-N-butylamino-7-(2xe2x80x2-fluoroanilino)fluoran,
3-pyrrolidyl-7-dibenzylaminofluoran,
3-bis(diphenylamino)fluoran,
3-diethylamino-7-(2xe2x80x2-chloroanilino)fluoran,
3-diethylamino-6-chloro-7-anilinofluoran,
3-dibutylamino-7-(2xe2x80x2-chloroanilino)fluoran,
3-diethylamino-7-chlorofluoran,
3-diethylamino-6-methyl-7-chlorofluoran,
3-N-methyl-N-cyclohexylamino-6-chlorofluoran,
3-diethylamino-6-methyl-7-(2xe2x80x2,4xe2x80x2-dimethylanilino)fluoran,
3-diethylamino-7-dibenzylaminofluoran,
3-butylamino-7-(2xe2x80x2-chloroanilino)fluoran, and
3-diethylamino-6-ethoxyethyl-7-anilinofluoran.
The composition comprising the aromatic carboxylic acid compounds according to the present invention may be used alone as the color developer in the thermosensitive recording material. Alternatively, the aforementioned composition may be used in combination with the conventional color developers. In this case, the composition of the present invention can also serve as, for example, a sensitizer.
Specific examples of the conventional color developers for use in the present invention are as follows:
4,4xe2x80x2-isopropylidenebisphenol,
4,4xe2x80x2-isopropylidenebis(o-methylphenol),
4,4xe2x80x2-sec-butylidenebisphenol,
4,4xe2x80x2-isopropylidenebis(2-tert-butylphenol),
zinc p-nitrobenzoate,
1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid,
2,2-(3,4-dihydroxyphenylpropane),
bis(4-hydroxy-3-methylphenylsulfide),
4-[xcex2-(p-methoxyphenoxy)ethoxy]salicylic acid,
1,7-bis(4-hydroxyphenylthio)-3,5-dioxaheptane,
monobenzyl phthalate monocarboxylic acid,
4,4xe2x80x2-cyclohexylidenebisphenol,
4,4xe2x80x2-isopropylidenebis(2-chlorophenol),
2,2xe2x80x2-methylenebis(4-methyl-6-tert-butylphenol),
4,4xe2x80x2-butylidenebis(6-tert-butyl-2-methyl)phenol,
1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexyl)butane,
4,4xe2x80x2-thiobis(6-tert-butyl-2-methylphenol),
4,4xe2x80x2-diphenolsulfone,
4-benzyloxy-4xe2x80x2-hydroxydiphenylsulfone, 4-isopropyloxy-4xe2x80x2-hydroxydiphenylsulfone,
4,4xe2x80x2-diphenolsulfoxide,
isopropyl p-hydroxybenzoate,
benzyl p-hydroxybenzoate,
benzyl protocatechuate,
stearyl gallate,
1,3-bis(4-hydroxyphenylthio)propane,
1,3-bis(4-hydroxyphenylthio)-2-hydroxypropane,
N,N-diphenylthiourea,
N,N-di(m-chlorophenylthiourea),
salicylanilide,
5-chlorosalicylanilide,
bis(4-hydroxyphenyl)methyl acetate,
bis(4-hydroxyphenyl)benzyl acetate,
1,3-bis(4-hydroxycumyl)benzene,
1,4-bis(4-hydroxycumyl)benzene,
2,4xe2x80x2-diphenolsulfone,
2,2xe2x80x2-diallyl-4,4xe2x80x2-diphenolsulfone,
3,4-dihydroxy-4xe2x80x2-methyldiphenylsulfone,
xcex1,xcex1-bis(4-hydroxyphenyl)-xcex1-methyltoluene,
4,4xe2x80x2-thiobis(2-methylphenol), and
4,4xe2x80x2-thiobis(2-chlorophenol).
According to the present invention, the thermosensitive coloring layer may further comprise a variety of thermofusible materials as a thermosensitivity-improving agent and a lubricant. In such a case, the thermofusible material may be used alone or in combination.
Specific examples of the thermofusible materials are as follows: fatty acids such as stearic acid and behenic acid; fatty amides such as stearamide and palmitamide; fatty acid metallic salts such as zinc stearate, aluminum stearate, calcium stearate, zinc palmitate, and zinc behenate; and p-benzylbiphenyl, terphenyl, triphenylmethane, benzyl p-benzyloxybenzoate, xcex2-benzyloxy naphthalene, phenyl xcex2-naphthoate, phenyl 1-hydroxy-2-naphthoate, methyl 1-hydroxy-2-naphthoate, diphenyl carbonate, benzyl terephthalate, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 1,4-dibenzyloxynaphthalene, 1,2-diphenoxyethane, 1,2-bis(4-methylphenoxyethane), 1,4-diphenoxy-2-butene, 1,2-bis(4-methoxyphenylthio)ethane, dibenzoylmethane, 1,4-diphenylthiobutane, 1,4-diphenylthio-2-butene, 1,3-bis(2-vinyloxyethoxy)benzene, 1,4-bis(2-vinyloxyethoxy)benzene, p-(2--vinyloxyethoxy)biphenyl, p-aryloxybiphenyl, dibenzoyloxymethane, dibenzoyloxypropane, dibenzyl disulfide, 1,1-diphenylethanol, 1,1-diphenylpropanol, p-benzyloxybenzyl alcohol, 1,3-phenoxy-2-propanol, N-octadecylcarbamoyl-p-methoxycarbonylbenzene, N-octadecylcarbamoylbenzene, 1,2-bis(4-methoxyphenoxy)propane, 1,5-bis(4-methoxyphenoxy)-3-oxapentane, dibenzyl oxalate, bis(4-methylbenzyl)oxalate, and bis(4-chlorobenzyl)oxalate.
When the thermosensitive recording material of the present invention is prepared, not only the above-mentioned color developer such as the composition of the aromatic carboxylic acid compounds, leuco dye, and thermofusible material, but also other materials for constituting the conventional thermosensitive recording material may be appropriately employed. For instance, a variety of binder agents for binding the materials for constituting the thermosensitive coloring layer to the support may be used. Such binder agents may be used alone or in combination.
Specific examples of the binder agent for use in the thermosensitive coloring layer include water-soluble polymers such as poly(vinyl alcohol), modified poly(vinyl alcohol), starch and starch derivatives, cellulose derivatives such as methoxy cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose, sodium polyacrylate, poly(vinylpyrrolidone), acrylamide-acrylic ester copolymer, acrylamide-acrylic ester-methacrylic acid terpolymer, alkali salts of styrene-maleic anhydride copolymer, alkali salts of isobutylene-maleic anhydride copolymer, polyacrylamide, modified polyacrylamide, methyl vinyl ether-maleic anhydride copolymer, carboxy-modified polyethylene, vinyl alcohol-acrylamide block copolymer, melamine-formaldehyde resin, urea-formaldehyde resin, sodium alginate, gelatin, and casein; emulsions such as poly(vinyl acetate), polyurethane, styrene-butadiene copolyer, styrene-butadiene-acrylic copolymer, poly(acrylic acid), polyacrylate, polymethacrylate, vinyl chloride-vinyl acetate copolymer, poly(butyl methacrylate), poly(vinyl butyral), poly(vinyl acetal), and ethylene-vinyl acetate copolymer.
The above-mentioned binder agents may be cured by the addition of a crosslinking agent (curing agent) when necessary. In this case, the crosslinking agent (curing agent) capable of reacting with the binder agents, for example, glyoxal derivatives, methylol derivatives, epichlorohydrin derivatives, epoxy compounds, and aziridine compounds are usable.
Furthermore, the thermosensitive coloring layer may further comprise a pigment.
Examples of the pigment for use in the thermosensitive coloring layer are finely-divided inorganic particles of silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, kaolin, calcined kaolin, talc, and surface-treated silica; and finely-divided organic particles of urea-formalin resin, styrene-methacrylic acid copolymer, polystyrene resin, vinylidene chloride resin, styrene-acrylic copolymer, and various kinds of plastic spherical minute void particles.
The thermosensitive recording material of the present invention may further comprise a protective layer which is overlaid on the thermosensitive coloring layer in order to improve the head-matching properties, that is, the matching properties of the thermosensitive recording material with a thermal head, enhance the preservation stability of the recorded images, and upgrade the writing and printing quality of the recording material.
The protective layer may comprises a pigment, a binder agent, a crosslinking agent, and a lubricant. The same pigments, binder agents, crosslinking agents, and lubricants (thermofusible material) as previously described are usable for the formation of the protective layer. With respect to each of these materials, such as the pigment or binder agent, one kind of material component may be used alone or two or more kinds of material components may be used in combination.
The thermosensitive recording material of the present invention may further comprise an undercoat layer which is interposed between the support and the thermosensitive coloring layer. The undercoat layer comprising as the main components a pigment and a binder agent can serve as a heat insulating layer. Namely, owing to the presence of the undercoat layer, thermal energy supplied to the thermosensitive recording material by the thermal head can be efficiently utilized, thereby improving the thermal sensitivity of the recording material. With respect to the pigment or binder agent for use in the undercoat layer, the above-mentioned pigment components or binder agent components may be independently used alone or in combination. In particular, it is desirable to use as the pigment plastic spherical void particles in the undercoat layer.
The plastic spherical void particles for use in the present invention comprise a thermoplastic resin for forming a shell of each void particle. Air or other gasses are contained in the void particles in the expanded state.
It is preferable that the average particle diameter (outer diameter) of the void particles be in the range of about 0.2 to 20 xcexcm. When the average particle size of the void particles is within the aforementioned range, there is no problem in the production because the voidage of the void particles can freely be determined. In addition, the surface smoothness of the undercoat layer obtained by coating is not excessively decreased. Therefore, the adhesion of the surface of the thermosensitive recording material to the thermal head does not lower, and consequently, deterioration of the thermal sensitivity of the recording material can be avoided. Further, it is preferable that the void particles classified in a narrow distribution be employed in the undercoat layer.
It is preferable that the voidage of the spherical void particles for use in the undercoat layer be 40% or more, and more preferably 90% or more, from the viewpoint of the heat insulating effect. When the voidage is within the above range, sufficient heat insulating effect of the undercoat layer can be obtained, so that the thermal energy supplied by the thermal head can be inhibited from escaping through the support of the thermosensitive recording material. As a result, the effect of improving the thermal sensitivity does not deteriorate.
In the present invention, the voidage of the plastic spherical void particles for use in the undercoat layer is expressed by the following formula:       Voidage    ⁢          xe2x80x83        ⁢          (      %      )        =                    (                  Inner          ⁢                      xe2x80x83                    ⁢          diameter          ⁢                      xe2x80x83                    ⁢          of          ⁢                      xe2x80x83                    ⁢          void          ⁢                      xe2x80x83                    ⁢          particle                )                    (                  Outer          ⁢                      xe2x80x83                    ⁢          diameter          ⁢                      xe2x80x83                    ⁢          of          ⁢                      xe2x80x83                    ⁢          void          ⁢                      xe2x80x83                    ⁢          particle                )              xc3x97    100  
Specific examples of the thermoplastic resin for forming a shell of the void particle are polystyrene, poly(vinyl chloride), poly(vinylidene chloride), poly(vinyl acetate), poly(acrylic ester), polyacrylonitrile, polybutadiene, and copolymer resins comprising the monomers for use in the above-mentioned resins. Of those thermoplastic resins, a copolymer resin comprising as the main component vinylidene chloride or acrylonitrile is preferably employed in the present invention.
A binder resin for the formation of the above-mentioned undercoat layer may be appropriately selected from the conventional water-soluble polymers and aqueous polymeric emulsions.
Specific examples of the binder agent for use in the undercoat layer are water-soluble polymers such as poly(vinyl alcohol), starch and starch derivatives, cellulose derivatives such as methoxy cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose and ethyl cellulose, sodium polyacrylate, poly(vinylpyrrolidone), acrylamidexe2x80x94acrylic ester copolymer, acrylamicexe2x80x94acrylic esterxe2x80x94methacrylic acid terpolymer, alkali salts of styrenexe2x80x94maleic anhydride copolymer, alkali salts of isobutylenexe2x80x94maleic anhydrice copolymer, polyacrylamide, sodium aliginate, gelatin, and casein; and aqueous polymeric emulsions including latexes such as styrenexe2x80x94butadiene copolymer and styrenexe2x80x94butadienexe2x80x94acryl copolymer, and emulsions such as vinyl acetate resin, vinyl acetatexe2x80x94acrylic acid copolymer, styrenexe2x80x94acrylic ester copolymer, acrylic ester resin, and polyurethane resin.
In the undercoat layer for use in the present invention, the previously mentioned plastic spherical void particles and binder resin may be used in combination with auxiliary additive components such as a filler, a thermofusible material, a surface active agent, and an agent for preventing color development by the application of pressure, which are used in the conventional thermosensitive recording materials. Specific examples of the filler and the thermofusible material for use in the undercoat layer are the same as those mentioned in the formation of the thermosensitive coloring layer. Further, when the plastic spherical void particles are contained in the undercoat layer, it is recommendable that an inorganic pigment be contained in the undercoat layer in order to improve the head-matching properties.
Furthermore, in the present invention, an intermediate layer comprising a pigment, a binder agent and a thermofusible material may be interposed between the undercoat layer and the thermosensitive coloring layer when necessary.
The thermosensitive recording material of the present invention may further comprise a backcoat layer which is provided on the back surface of the support, opposite to the thermosensitive coloring layer with respect to the support. The backcoat layer may comprise the same pigment, binder agent, and lubricant (thermofusible material) as mentioned above.
As the support of the thermosensitive recording material, a sheet of plain paper, such as acidic paper and alkaline paper, and other support members on which a coating liquid can be coated may freely be used. For example, a sheet of synthetic paper and a polymeric film are usable as the support.
The thermosensitive recording material of the present invention is applicable in any fields that employ the conventional thermosensitive recording materials. For instance, the thermosensitive recording material can be used as a paper for facsimile machine, a point-of-sales (POS) label for food, a bar code label for industrial applications, a thermosensitive recording adhesive label of liner-less type, a ticket paper, a magnetic ticket paper, a paper for CAD, and a transparent thermosensitive film.
Other features of this invention will become apparent in the course of the following description of exemplary embodiments, which are given for illustration of the invention and are not intended to be limiting thereof.